Neighboring group effect directive

The use of metals for prearranging reaction centers as neighboring groups has a special value in the production of macrocycles (template effect). Although these ligands can be sometimes prepared directly, the addition of metal ion during the synthesis will often increase the yield, modify the stereochemical nature of the product, or even be essential in the buildup of the macrocycle. There have been few mechanistic studies of these processes. The alkali and alkaline-earth metal ions can promote the formation of benzo[18]crown-6 in methanol ... 

In organic chemistry it is well known that a substituent directly linked to a reaction center has a profound effect on the latter s reactivity. The influence of a remote substituent has also received much attention as more organic molecules are being scrutinized. Thus, neighboring group participations in solvolysis are generally observed. Certainly, the full attribution of a substituent must be the sum of electronic, steric, and stereoelectronic factors. 

---